Written by experts who pioneered use of genetic data to search for the aggressive fish, the paper disagrees with government scientists who say many of the positive Asian carp DNA hits recorded in or near the lakes in recent years could have come from other sources, such as excrement from birds that fed on carp in distant rivers.
"The most plausible explanation is still that there are some carp out there," Christopher Jerde
of the University of Notre Dame, the lead author, told The Associated
Press in a telephone interview. "We can be cautiously optimistic ...
that we're not at the point where they'll start reproducing, spreading
further and doing serious damage."
The paper summarizes findings by Jerde and other scientists from
Notre Dame, The Nature Conservancy and Central Michigan University
during two years of searching the Great Lakes basin for Asian carp. The
fish have migrated northward in the Mississippi River and many
tributaries since escaping from Deep South ponds in the 1970s.
Scientists fear they will out-compete prized sport and commercial
species.Of particular concern are silver and bighead carp, which gorge on plankton — microscopic plants and animals that virtually all fish eat at some point. The carp reproduce prolifically, and the biggest can reach 100 pounds.
Between September 2009 and
October 2011, Jerde and his colleagues collected more than 2,800 water
samples from parts of the Great Lakes and tributary rivers. The samples
were poured through microfiber filters to extract DNA, which fish shed
in their excrement, scales and body slime. It's known as environmental DNA, or "eDNA."
Laboratory analysis turned up 58 positive hits for bighead or silver carp in the Chicago Area Waterway System — a network of rivers and canals linked directly to Lake Michigan — and six in western Lake Erie. Some of the Chicago DNA was found in Lake Calumet, where a live bighead carp was caught in 2010.
"I would say there's at least some evidence for Asian carp being
present in southern Lake Michigan," Jerde said. "The question is how
many."More recently, sampling by the U.S. Army Corps of Engineers and other federal agencies also yielded positive results in the Chicago waterways. But while the government team acknowledges the presence of Asian carp genetic fingerprints, it disagrees that they necessarily signal the presence of live fish.
The issue is significant because
it could influence the debate over whether to seal off Lake Michigan
from the Chicago waterways, a mammoth engineering task that would cost
billions of dollars and take years to complete. Five states sought that
step in a lawsuit dismissed by a federal judge last December. Under
pressure from Congress, the Army Corps of Engineers has pledged to offer
options for preventing species migrations between the Great Lakes and
the Mississippi River watershed later this year.
The Army Corps
contends an electric barrier in a canal 37 miles from Chicago is
preventing the carp from getting through, even though their DNA has
turned up repeatedly on the other side. In a February report, federal
agencies said the genetic material could have been transported by bird
feces, fish sampling gear, barges and storm sewers.
But the Jerde team's paper, published online Thursday by the Canadian
Journal of Fisheries and Aquatic Sciences, argues that the likeliest
explanation remains the presence of live Asian carp. It's probably no
coincidence that many of the positive samples have come from Chicago's
Lake Calumet and western Lake Erie, where three bigheads were snagged in
1995 and 2000, the paper says.It says the scientists found no signs of the carp in Chicago locations where they should have been abundant, such as sewer outfalls, if the alternative explanations were accurate.
The secondary alternatives are even less plausible for Lake Erie, the paper says. The DNA that was found there was more than 100 miles from waterways infested with Asian carp. So if birds were the source, it seemingly would mean they feasted on carp, flew a long distance and excreted feces within a few hours of when the researchers collected water samples.
"You're requiring all kinds of
random events to happen simultaneously," said Lindsay Chadderton of The
Nature Conservancy, who contributed to the paper. "It's possible, but
highly unlikely."
Kelly Baerwaldt, a fisheries biologist and Asian carp program manager
for the Army Corps who supports the alternative-source theory, said the
new report didn't change her mind. Fish-gobbling birds such as
cormorants often range over hundreds of miles, she said. And if live
carp are the only source of the DNA in Chicago, why has just one been
found beyond the electric barrier? (Jerde says they're notoriously hard
to catch.)"Sure, it could be live fish and it also could be these other things, because we tested them and looked at the evidence," Baerwaldt said.
The Army Corps, the U.S. Fish and Wildlife Service and the U.S. Geological Survey continue to study the issue and hope within a couple of years to refine methods of determining the likely source of a particular DNA sample, she said.
"The bottom line is there's just a lot we don't know about eDNA," she said. LINK
Posts
